USB: make transfer_buffer_lengths in struct urb field u32

Roel Kluin pointed out that transfer_buffer_lengths in struct urb was
declared as an 'int'.  This patch changes this field to be 'u32' to
prevent any potential negative conversion and comparison errors.

This triggered a few compiler warning messages when these fields were
being used with the min macro, so they have also been fixed up in this
patch.

Cc: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/usb/gadget/dummy_hcd.c b/drivers/usb/gadget/dummy_hcd.c
index 3b42888..a56b24d 100644
--- a/drivers/usb/gadget/dummy_hcd.c
+++ b/drivers/usb/gadget/dummy_hcd.c
@@ -1437,7 +1437,7 @@
 					}
 					if (urb->transfer_buffer_length > 1)
 						buf [1] = 0;
-					urb->actual_length = min (2,
+					urb->actual_length = min_t(u32, 2,
 						urb->transfer_buffer_length);
 					value = 0;
 					status = 0;